2

Great Transformations

Fossil whales. Similarities
in limb bones. The transition from water to land animals. A "genetic
toolkit" common to all animals. The transition from apes to humans.

A. Humans: A Recent
Branch on the Tree of Life

This second episode sets
out to answer some big questions: "Who are we? Where do we
come from? How did we get here? Why do we look the way we do?"

"The story of human
evolution," we are told, "is really just a small chapter
in a much larger story--the story of all living things." As
University of Chicago paleontologist Neil H. Shubin puts it: "Evolution
shows us that we're much more connected to the rest of the world,
the rest of animal life--than we could ever have imagined."

Accompanied by beautiful
photography of wild animals, and shots of scientists chipping away
at rocks or peering through microscopes, the narrator continues:
"The deeper we dig, the farther back we go, the more we see
that everything alive has evolved from a single starting-point.
The tree of life has been branching for four billion years, and
we can now follow the branches back to their roots."

As the camera focuses
on the fossilized fin of an ancient fish lying next to the bones
of a human arm, Shubin says: "When we look back over time,
we find certain signposts, certain key events--the great transformations,
the big evolutionary steps." Then, as a whale rises majestically
out of the water, the narrator explains: "Fifty million years
ago, land mammals were transformed into sea creatures. Long before
that, fish colonized land. At the dawn of animal life itself, the
very first bodies appeared. These are just some of the chapters
in life's story--our story."

After learning that all
of human existence is only a brief moment at the end of a very long
history of life, we are told that even though we are latecomers
"we have been shaped by the same forces that have shaped all
living things. To understand how we fit in, we need to look back
to long before our own origins, and see how evolution has shaped
other living things."

B. Whale Evolution

The scene shifts to whales
gliding effortlessly beneath the waves, and the narrator tells us
that their origin "was a mystery." According to University
of Michigan paleontologist Philip D. Gingerich, "whales are
so different from every other kind of mammal that we can't easily
relate them to anything else, and so they're off by themselves as
a branch of mammal evolution."

As air-breathers, mammals
live mostly on land; but whales and dolphins are mammals that live
in water. "But we know that mammals evolved on land,"
Shubin says, "so it's a real puzzle how whales originally evolved.
By understanding how that happens, we'll begin to understand how
these big jumps--these big transformations--happen generally."

Gingerich explains how
he discovered--and identified--the fossilized bones of a whale-like
creature in Pakistan. His search for what scientists call "transitional
forms" between land animals and whales later took him to the
Sahara Desert, which used to be covered by water. There he discovered
numerous fossils of a previously discovered extinct whale, Basilosaurus.
But Gingerich, unlike those who had gone before him, found tiny
leg bones with the fossils--thereby showing that Basilosaurus was
a whale with legs.

The narrator explains
that the land-dwelling ancestors of modern whales might have found
food and safety in the water of an ancient sea: "Over millions
of years, front legs became fins, rear legs disappeared, bodies
lost fur and took on their familiar streamlined shape." The
list of transitional forms between ancient land animals and modern
whales, we are told, has grown, proving that "the evidence
for evolution is all around us, if we choose to look for it."

Ignoring the fact that
the transitional series isn't as neat as it is portrayed here, there
are at least two problems with interpreting these fossils as evidence
for Darwinian evolution. First, it is impossible to determine whether
one fossilized species is ancestral to another. According to Henry
Gee, chief science writer for Nature, "the intervals of time
that separate fossils are so huge that we cannot say anything definite
about their possible connection through ancestry and descent."
The fossils examined in this episode are separated by millions of
years and thousands of generations. But it's hard enough to determine
who our own great-great-great grandparents are, even though they
are of the same species, the time span is measured in hundreds of
years, and we have written records to help us. We can only
assume that these intermediate fossil forms were connected
by a chain of ancestry and descent.

And that mechanism has
to be demonstrated with more plausibility--not to mention evidence--than
we see here. To claim merely that "front legs became fins,
rear legs disappeared, bodies lost fur and took on their familiar
streamlined shape" is not good enough. We have no evidence
from modern animals that front legs can become fins, or that a body
can assume a radically different shape--much less that a land animal
can make the numerous physiological changes it would need for life
in the water. Fossils of extinct animals do not necessarily show
us descent from a common ancestor, nor do they show us that the
change was due to Darwinian natural selection acting on random variations.

The scene changes to
an aquarium, where we are told that "bones aren't the only
evidence for whale evolution. Their ancestry is also visible in
the way they move." The fact that marine mammals propel themselves
through the water with up-and-down movements instead of the side-to-side
movements characteristic of fish is supposed to indicate their descent
from land mammals. But perhaps this is just a common feature of
mammals, like air breathing or bearing live young. How does the
fact that marine mammals move like other mammals provide evidence
for Darwinian evolution?

Neil Shubin returns to
conclude the story of whale evolution. "In one sense, evolution
didn't invent anything new with whales," he says, "it
was just tinkering with land mammals. It's using the old to make
the new, and we call that tinkering."

Sort of like what people
do with automobiles?

C. Moving onto the
Land

Land animals came before
whales, but fish came before land animals. So the great transformation
that produced land animals preceded the one that produced whales.
"It was the moment when fish crawled out of the water."

"The first creatures
to leave the water really started something," the narrator
explains. "Their ancestors eventually evolved into today's
reptiles, birds, and mammals. And these creatures' common origins
are still visible in their bodies. Just like us, they all have bodies
with four limbs--they're all tetrapods."

Neil Shubin jumps in
again: "What that means is that all these different creatures
are descended from a common ancestor which had something very similar,
or akin, to limbs."

"Just what was that
common ancestor," the narrator asks, "and how did it leave
the water 370 million years ago?" Shubin and his colleagues
find fossils in Pennsylvania suggesting that early tetrapods lived
in streams, while Cambridge University paleontologist Jenny Clack
finds fossils in Greenland suggesting that fish evolved limbs before
they left the water.See
. For the standard story, see:

Shubin points to the
fossil fish fin and human arm skeleton that we saw at the beginning
of the episode, and he notes the similarity in the arrangements
of their bones. According to the narrator: "With the basic
pattern in place, the fin-to-limb transition was merely a series
of small changes occurring over millions of years." And a cartoon
animation shows us how easy this might have been. But a cartoon
animation, no matter how plausible, does not show how real animals
in real time could have been transformed from fish into land animals.

Shubin continues: "There's
really no goal to evolution. Evolution wasn't trying to make limbs;
it wasn't trying to push our distant ancestors out of the water.
What was happening was a series of experiments." And the narrator
concludes: "Fish experimented with all sorts of survival strategies.
. . . The first tetrapods possibly found another way to survive"--by
getting out of the water.

So fish "experimented"
with survival "strategies" that included growing legs.
But clever human biologists have been experimenting with fish for
years, and they have not come up with a strategy to make fish grow
even the beginnings of legs. What sense does it make to say that
fish "experimented" with growing legs?

The truth is that scientists
don't know how the first legs--or the first tetrapods, or the first
air-breathers, or the first whales--originated. The fossils tell
us that aquatic animals preceded land animals, and that land animals
preceded whales. On the question of what caused these great transformations,
however, the fossils are silent.

But without knowing what
caused these great transformations, how can Shubin say with such
confidence that evolution had no goal? How does he know?

D. The Cambrian Explosion

As the camera pans over
the fossilized remains of ancient animals, the narrator says: "The
water-to-land transformation wasn't the first time evolution had
experimented with radical new forms of life. An even earlier explosion--perhaps
the most significant of all--occurred just over half a billion years
ago. This was the one that led to animal life itself."

Shubin elaborates: "Evolution
tinkered with fish to make limbs, but fish carry the baggage of
their own past. Think of a fish. It has a head, it has a tail, and
a bunch of fins in between. That's a body plan--the way the body's
put together. But that's just one of many ways of putting animals
together." We're shown pictures of jellyfish, a millipede,
a beetle, and a crab. "The question is: What sort of tinkering
led to these body plans? I mean really what we're dealing with here
is the origin of animals."

"According to the
fossil record," the narrator says, "animals burst upon
the earth rather suddenly," hundreds of millions of years ago.
"Scientists call this crucial transformation the Cambrian explosion."
Cambridge University paleontologist Simon Conway Morris explains:
"The Cambrian explosion was effectively one of the greatest
breakthroughs in the history of life. About half a billion years
ago, suddenly things change, we have this extraordinary explosion
of diversity. And this sudden appearance of the fossils led to this
term, the Cambrian explosion. Darwin, as ever, was extremely candid--he
said, Look, this is a problem for my theory. How is it that suddenly
animals seem to come out of nowhere? And to a certain extent that
is still something of a mystery."

It certainly is. In Darwin's
theory, all animals are descended from a common ancestor. If the
theory were true, we would expect the history of animal life to
begin with one form; as time passes, this form would give rise to
two or three that are only slightly different from each other; and
with more time, these would give rise to other forms, even more
different from each other. Finally, after millions of generations,
we would see the major differences that now separate clams from
starfish and insects from vertebrates.

The coverage of the Cambrian
explosion in this episode is better than one usually sees in treatments
of evolution. Most biology textbooks (including one co-authored
by Kenneth Miller, who played a prominent role in Episode One),
completely ignore the Cambrian explosion and the challenge it poses
to Darwin's theory. Evolution's producers deserve to be commended
for including it, though they largely ignore Simon Conway Morris's
comment that the Cambrian explosion "is still something of
a mystery," and thus pass up a chance to acquaint viewers with
the controversy surrounding one of evolution's most exciting unresolved
challenges.

Spectacular views of
the Canadian Rockies now follow--home of the famous Burgess Shale,
which has provided us with much of the best evidence for the Cambrian
explosion. After surveying some of the forms found in the Burgess
Shale, the narrator says: "All the basic body plans found in
nature today are here. Everything that has lived for the last half-billion
years came from tinkering with these initial designs. We can even
see our own ancestor here." Simon Conway Morris displays a
photograph of a tiny worm, Pikaia, and tells us "this might
be the precursor of the fish, and so also, I believe--after a long
evolutionary story--ourselves."

Neil Shubin returns to
summarize what we've seen so far: "So what do we learn by looking
at 600 million years of animal history? Evolution's tinkering with
mammalness to make whales; in the same way, it's tinkering with
fishiness to make tetrapods; and it's tinkering with animalness
to make all the different body plans that we see."

There's that "tinkering"
again. We've seen that animals burst upon the scene rather suddenly,
that land animals came later, and that whales came later still.
Things are certainly not what they used to be. But where is the
evidence that it all happened through "tinkering"?

Shubin continues: "All
these different creatures are variations of the same theme, re-stated
over and over again. The question was, What was evolution tinkering
with? One of the remarkable discoveries of the last twenty years
is that evolution's not tinkering with the bodies, it's tinkering
with the recipe, the machinery that builds bodies. What is that
recipe? What is that machinery? It's the genes, the genes that build
them."

Finally, we are promised
some hard evidence of how these great transformations took place.
Let's take a look at it.

E. The Genetic Mechanism
of Evolution

"Fossils record
the changes in animals' bodies over time," the narrator says,
"but just how bodies changed was
unknown. The search for the genetic mechanism of evolution took
most of the century. When scientists finally found it, they were
astonished by just how simple it was."

In the nineteenth century,
geneticist William Bateson had observed that embryos would occasionally
develop body parts in the wrong places. Then biologists in the 1940s
discovered that they could produce such effects in fruit flies by
using radiation. Stanford University developmental biologist Matthew
P. Scott explains that, like Bateson, these researchers would occasionally
find flies with "one part of the body in the wrong place, or
a copy of a normal part of the body in another place."

Watch closely as a fruit fly with an extra pair of wings fills
the screen. (Fruit flies normally have two wings, but this one has
four.) Note that the wing visible here behind the normal pair is
stiff and motionless. That's because the second pair of wings has
no muscles. The extra wings are thus useless, and the fly has difficulty
flying and mating--though that fact goes unmentioned here. Next
we see a mutant fly with no wings (which of course has even more
difficulty flying!), then a fly with stubby legs instead of antennae
growing out of its head. All three of these mutant flies are cripples,
and cannot survive long outside the laboratory.

"The scientists
had triggered the changes by damaging the fly's DNA," the narrator
says. He continues with an overview of how scientists in the past
quarter-century have unraveled some of the ways in which genes affect
embryo development. It's a fascinating story about painstaking research,
requiring considerable patience and perseverance, which finally
ended in success. One of those successes involved deciphering the
action of the Antennapedia gene, in which mutations can cause flies
to sprout legs from their heads. The narrator concludes that the
"implications were mind-boggling," because such genes
seemed to be "acting like architects of the body."

Could this discovery
be generalized to other animals? The scene switches to Switzerland,
where University of Basel cell biologist Walter Gehring describes
how he removed a gene from a fruit fly that is needed for normal
eye development, and inserted a comparable gene from a mouse. Gehring
found that the mouse gene did the work of the fly gene. "The
fruit fly had grown normal fruit fly eyes," the narrator explains,
"using a gene from a mouse. Not only did the two creatures
use the same mechanism--they used the very same gene. This was the
mechanism behind extra wings, legs sprouting from heads, and Bateson's
deformed animals. The century-long search was complete. The genetic
engine of evolution turned out to be a tiny handful of powerful
genes."

As we watch some more
beautiful wildlife photography, University of Wisconsin geneticist
Sean B. Carroll interprets the significance of this: "So what
this means is--in some ways, some sense--evolution is a simpler
process than we first thought. When you think about all of the diversity
of forms out there, we first believed that this would involve all
sorts of novel creations, starting from scratch, again and again
and again. We now understand that, no, that evolution works with
packets of information, and uses them in new and different ways
and new and different combinations without necessarily having to
invent anything fundamentally new, but new combinations."

As a series of brightly-colored
cartoons shows the supposedly similar body organization of various
kinds of animals, the narrator explains: "Suddenly, the commonality
of form among animals was understood. Animals resembled each other
because they all used the same set of genes to build their bodies--a
set of genes inherited from a common ancestor that lived long ago."
Matthew Scott adds: "And what we see now among all the animals
are just variations on a body plan that existed half a billion years
ago."

"And there's only
one inescapable conclusion you can draw from that," says Carroll,
"which is: If all of these branches have these genes, then
you have to go to the base of that, which is the last common ancestor
of all animals, and you deduce it must have had these genes. So
the whole radiation of animals, the whole spring of animal diversity
has been fed by essentially the same set of genes."

What's wrong with this
picture? The story we have just heard ignores two fundamental problems.
The first is that (as we saw above) the genetic changes shown here
are--without exception!--harmful to the organism. In the wild, all
of these changes would be quickly eliminated by natural selection.
Geneticists have learned a lot about how genes affect embryo development,
but they have not yet found a single mutation that changes the shape
of an animal's body in a way that might be useful for evolution
outside the laboratory. (Useful mutations occur in some cases of
antibiotic resistance, as we shall see in Episode Four; but that's
a far cry from changing the shape of an animal's body.)

The second problem is
that the "tiny handful of powerful genes" is nowhere near
as powerful as we are led to believe. Note that the mouse eye gene
inserted into the fruit fly produced a fruit
fly eye, not a mouse eye. In other words, the gene was not
the "architect" of the eye; it merely acted as a switch,
enabling the animal to make an eye when and where it needed one.
But the gene has nothing to do with the kind of eye the animal makes.
It's more like an electrical switch that can turn on a light, a
computer, a vacuum cleaner--or whatever else is plugged into it.
If these genes are what animals use to "build their bodies,"
and if all animals have the same set of genes, how come the various
kinds of animals are so different from each other? Why don't fruit
flies give birth to finches?

Once again, we are left
without the evidence we were hoping to see. Instead, we are simply
assured that evolution is simpler than we thought, and given the
same line that modern animals are simply variations of an ancestral
body plan that existed long ago.

F. From Ape to Human

"What about us?"
the narrator asks. "Our bodies are built from the same genes
that build all other animals. Yet we are different. No other animal
designs or creates like we do." The camera pans slowly over
Michelangelo's Sistine Chapel painting of God touching Adam. The
narrator continues: "We seem so special, it's hard not to think
that we're somehow an exception to evolution. But of course we're
not. The transformation that led to us was no different from the
others." In a familiar scene (which is repeated again and again
throughout the series), an ape clambers down a log to the ground.
"The crucial turning-point seems to have occurred about seven
million years ago, when our ancestors left the trees and began to
walk on two legs."

According to Arizona
State University paleoanthropologist Donald Johanson, this probably
first happened in East Africa. He and the narrator explain how walking
on two feet seems to have opened the door to the evolution of our
brains, though little is known about how our ancestors became bipeds.
University of Texas anthropologist Liza J. Shapiro tries to answer
this question by studying lemurs, because "we have to know
what it was we started from." The narrator explains: "Like
lemurs, our early ancestors could move in all sorts of ways."
So "they were already adapted to so many movement styles, they
could serve as the starting-point for a variety of evolutionary
experiments. And that's just what happened."

After being assured that
we evolved from a lemur-like animal, and that the striking similarities
between chimps and us show that we only recently evolved from a
common ancestor, we are told that "the few physical differences
that set us apart seem to have made a great difference." Johanson
points out some of them on models of human and chimp skeletons,
and concludes: "These are minor differences. These are the
sorts of tinkering that evolution did to change us into a modern
biped." So "what we see is that evolution has worked the
same way with us as it has with every single organism on this planet.
We're here through a series of chance coincidences, specific adaptations,
chosen opportunities."

Words like "tinkering"
and "chance" clearly mean something other than what Michelangelo
painted on the ceiling of the Sistine Chapel. But--once again--where
is the evidence? That we are "built from the same genes that
build all other animals"? That lemurs can "move in all
sorts of ways"? That there are both similarities and differences
between humans and chimps?

The truth is that the
evidence for human origins is even weaker than some of the other
evidence we've seen. According to Henry Gee, chief science writer
for Nature, all the evidence for human evolution "between about
10 and 5 million years ago--several thousand generations of living
creatures--can be fitted into a small box." Thus the conventional
picture of human evolution as lines of ancestry and descent is "a
completely human invention created after the fact, shaped to accord
with human prejudices." Putting it even more bluntly, Gee concludes:
"To take a line of fossils and claim that they represent a
lineage is not a scientific hypothesis that can be tested, but an
assertion that carries the same validity as a bedtime story--amusing,
perhaps even instructive, but not scientific."See
. For the Gee quotations see: Henry Gee, In Search of Deep Time
(New York: The Free Press, 1999), 23, 32, 113-117, 202.

So Episode Two, instead
of showing us the "underlying evidence" for Darwin's theory,
leaves us with a bedtime story.

Notes

.
Not surprisingly, the actual story of whale-like fossils is not
as neat as the one told here. There are long-standing disputes
over the identity of the land ancestor, the geological position
of various fossils, and whether these were the ancestors of modern
whales. Modern molecular studies have added to the controversy.
For a short survey of some of the disputes, see Ashby L. Camp,
"The Overselling of Whale Evolution," available at:

http://www.trueorigins.org/whales.htm#top.

See also:

http://www.sciencenews.org/sn_arc98/10_10_98/Fob3.htm

For more
on how modern molecular studies have added to the controversy,
see Trisha Gura, "Bones, molecules . . . or both?" Nature
406 (2000), 230-233; Maureen A. O'Leary, "Parsimony Analysis
of Total Evidence from Extinct and Extant Taxa and the Cetacean-Artiodactyl
Question (Mammalia, Ungulata)," Cladistics 15 (1999), 315-330.
See also:

http://www.findarticles.com/m1200/19_156/57828404/p1/article.jhtml

On the impossibility
of inferring ancestor-descendant relationships from fossils see
Henry Gee, In Search of Deep Time (New York: The Free Press, 1999).
Some passages from Gee's book that deal with human evolution are
cited below in the note on human origins.

On the fact
that mere similarity is insufficient to establish Darwinian descent
with modification, see Jonathan Wells and Paul Nelson, "Homology:
A Concept in Crisis," available at:

http://www.arn.org/docs/odesign/od182/hobi182.htm

Of course,
the true story is more complicated than the one presented in this
episode; see Michel Laurin, Marc Girondot and Armand de Ricqlès,
"Early tetrapod evolution," Trends in Ecology and Evolution
15 (2000), 118-123.

The "tinkering"
metaphor comes from François Jacob, "Evolution and
Tinkering," Science 196 (1977), 1161-1166. According to Jacob,
an engineer works according to a preconceived plan, uses prepared
materials and special machines, and produces things that are as
nearly perfect as possible. Evolution, on the other hand, has
no plan, works with whatever is at hand, and produces things that
are imperfect. But a tinkerer still works according to a plan,
though it may be a short-range plan (i.e., to make something useful);
and the history of technology is filled with examples of engineered
products that were notably imperfect. Most importantly, the sort
of creative capacity attributed to natural selection by the tinkering
metaphor has never been observed in nature.

.
Darwin wrote in The Origin of Species that "if the theory
be true, it is indisputable that before the lowest Cambrian
stratum was deposited long periods elapsed . . . [in which]
the world swarmed with living creatures." Yet he acknowledged
that "several of the main divisions of the animal kingdom
suddenly appear in the lowest known fossiliferous rocks."
Darwin called this a "serious" problem which "at
present must remain inexplicable; and may be truly urged as
a valid argument against the views here entertained." (Chapter
X; page numbers will vary depending on the edition.)

Simon Conway
Morris has written about the Burgess Shale in The Crucible of
Creation: The Burgess Shale and the Rise of Animals (Oxford: Oxford
University Press, 1998). So has Stephen Jay Gould, in Wonderful
Life: The Burgess Shale and the Nature of History ((New York:
W. W. Norton, 1989). See also Simon Conway Morris and H. B. Whittington,
"The Animals of the Burgess Shale," Scientific American
241 (1979), 122-133; Mark and Dianna McMenamin, The Emergence
of Animals: The Cambrian Breakthrough (New York: Columbia University
Press, 1990); Jeffrey S. Levinton, "The Big Bang of Animal
Evolution," Scientific American 267 (1992), 84-91; and J.
Madeleine Nash, "When Life Exploded," Time (December
4, 1995), 66-74.

For a more
extended discussion of the challenge posed by the Cambrian explosion
to Darwin's theory, see Jonathan Wells, Icons of Evolution (Washington,
DC: Regnery Publishing, 2000), Chapter 3. In contrast, one biology
textbook that covers the topic of evolution but manages to ignore
the Cambrian explosion completely is Kenneth R. Miller and Joseph
Levine, Biology (Upper Saddle River, NJ: Prentice-Hall, 2000).

.
For a detailed discussion of the problems with using four-winged
fruit flies as evidence for evolution, see Jonathan Wells, Icons
of Evolution (Washington, DC: Regnery Publishing, 2000), Chapter
9.

For some
general critiques of the idea that "genes build bodies,"
see H. F. Nijhout, "Metaphors and the Role of Genes in Development,"
BioEssays 12 (1990), 441-446; Brian Goodwin, How the Leopard Changed
Its Spots (New York: Charles Scribner's Sons, 1994); Steven Rose,
Lifelines (Oxford: Oxford University Press, 1997); and Jason Scott
Robert, "Interpreting the homeobox: metaphors of gene action
and activation in development and evolution," Evolution &
Development 3:4 (2001), 287-295.

According
to paleoanthropologist Misia Landau, many writings in her field
have been "determined as much by traditional narrative frameworks
as by material evidence." The typical framework is that of
a folktale in which a hero (i.e., our ancestor) leaves a relatively
safe haven in the trees, sets out on a dangerous journey, acquires
various gifts, survives a series of tests, and is finally transformed
into a true human being. When paleoanthropologists want to explain
what really happened in human evolution they use four main events.
These are: moving from trees to the ground, developing upright
posture, acquiring intelligence and language, and developing technology
and society. Although Landau found these four elements in all
accounts of human evolution, their order varied depending on the
viewpoint of the narrator. She concluded that "themes found
in recent paleoanthropological writing . . . far exceed what can
be inferred from the study of fossils alone and in fact place
a heavy burden of interpretation on the fossil record--a burden
which is relieved by placing fossils into preexisting narrative
structures." Narratives of Human Evolution (New Haven, CT:
Yale University Press, 1991), ix-x, 148.

In 1997,
Arizona State University anthropologist Geoffrey Clark wrote that
"we select among alternative sets of research conclusions
in accordance with our biases and preconceptions--a process that
is, at once, both political and subjective." Clark suggested
"that paleoanthropology has the form but not the substance
of a science." G. A. Clark and C. M. Willermet (eds.), Conceptual
Issues in Modern Human Origins Research (New York: Aldine de Gruyter,
1997), 76.

2

Great Transformations

Fossil whales. Similarities
in limb bones. The transition from water to land animals. A "genetic
toolkit" common to all animals. The transition from apes to humans.

A. Humans: A Recent
Branch on the Tree of Life

This second episode sets
out to answer some big questions: "Who are we? Where do we
come from? How did we get here? Why do we look the way we do?"

"The story of human
evolution," we are told, "is really just a small chapter
in a much larger story--the story of all living things." As
University of Chicago paleontologist Neil H. Shubin puts it: "Evolution
shows us that we're much more connected to the rest of the world,
the rest of animal life--than we could ever have imagined."

Accompanied by beautiful
photography of wild animals, and shots of scientists chipping away
at rocks or peering through microscopes, the narrator continues:
"The deeper we dig, the farther back we go, the more we see
that everything alive has evolved from a single starting-point.
The tree of life has been branching for four billion years, and
we can now follow the branches back to their roots."

As the camera focuses
on the fossilized fin of an ancient fish lying next to the bones
of a human arm, Shubin says: "When we look back over time,
we find certain signposts, certain key events--the great transformations,
the big evolutionary steps." Then, as a whale rises majestically
out of the water, the narrator explains: "Fifty million years
ago, land mammals were transformed into sea creatures. Long before
that, fish colonized land. At the dawn of animal life itself, the
very first bodies appeared. These are just some of the chapters
in life's story--our story."

After learning that all
of human existence is only a brief moment at the end of a very long
history of life, we are told that even though we are latecomers
"we have been shaped by the same forces that have shaped all
living things. To understand how we fit in, we need to look back
to long before our own origins, and see how evolution has shaped
other living things."

B. Whale Evolution

The scene shifts to whales
gliding effortlessly beneath the waves, and the narrator tells us
that their origin "was a mystery." According to University
of Michigan paleontologist Philip D. Gingerich, "whales are
so different from every other kind of mammal that we can't easily
relate them to anything else, and so they're off by themselves as
a branch of mammal evolution."

As air-breathers, mammals
live mostly on land; but whales and dolphins are mammals that live
in water. "But we know that mammals evolved on land,"
Shubin says, "so it's a real puzzle how whales originally evolved.
By understanding how that happens, we'll begin to understand how
these big jumps--these big transformations--happen generally."

Gingerich explains how
he discovered--and identified--the fossilized bones of a whale-like
creature in Pakistan. His search for what scientists call "transitional
forms" between land animals and whales later took him to the
Sahara Desert, which used to be covered by water. There he discovered
numerous fossils of a previously discovered extinct whale, Basilosaurus.
But Gingerich, unlike those who had gone before him, found tiny
leg bones with the fossils--thereby showing that Basilosaurus was
a whale with legs.

The narrator explains
that the land-dwelling ancestors of modern whales might have found
food and safety in the water of an ancient sea: "Over millions
of years, front legs became fins, rear legs disappeared, bodies
lost fur and took on their familiar streamlined shape." The
list of transitional forms between ancient land animals and modern
whales, we are told, has grown, proving that "the evidence
for evolution is all around us, if we choose to look for it."

Ignoring the fact that
the transitional series isn't as neat as it is portrayed here, there
are at least two problems with interpreting these fossils as evidence
for Darwinian evolution. First, it is impossible to determine whether
one fossilized species is ancestral to another. According to Henry
Gee, chief science writer for Nature, "the intervals of time
that separate fossils are so huge that we cannot say anything definite
about their possible connection through ancestry and descent."
The fossils examined in this episode are separated by millions of
years and thousands of generations. But it's hard enough to determine
who our own great-great-great grandparents are, even though they
are of the same species, the time span is measured in hundreds of
years, and we have written records to help us. We can only
assume that these intermediate fossil forms were connected
by a chain of ancestry and descent.

And that mechanism has
to be demonstrated with more plausibility--not to mention evidence--than
we see here. To claim merely that "front legs became fins,
rear legs disappeared, bodies lost fur and took on their familiar
streamlined shape" is not good enough. We have no evidence
from modern animals that front legs can become fins, or that a body
can assume a radically different shape--much less that a land animal
can make the numerous physiological changes it would need for life
in the water. Fossils of extinct animals do not necessarily show
us descent from a common ancestor, nor do they show us that the
change was due to Darwinian natural selection acting on random variations.

The scene changes to
an aquarium, where we are told that "bones aren't the only
evidence for whale evolution. Their ancestry is also visible in
the way they move." The fact that marine mammals propel themselves
through the water with up-and-down movements instead of the side-to-side
movements characteristic of fish is supposed to indicate their descent
from land mammals. But perhaps this is just a common feature of
mammals, like air breathing or bearing live young. How does the
fact that marine mammals move like other mammals provide evidence
for Darwinian evolution?

Neil Shubin returns to
conclude the story of whale evolution. "In one sense, evolution
didn't invent anything new with whales," he says, "it
was just tinkering with land mammals. It's using the old to make
the new, and we call that tinkering."

Sort of like what people
do with automobiles?

C. Moving onto the
Land

Land animals came before
whales, but fish came before land animals. So the great transformation
that produced land animals preceded the one that produced whales.
"It was the moment when fish crawled out of the water."

"The first creatures
to leave the water really started something," the narrator
explains. "Their ancestors eventually evolved into today's
reptiles, birds, and mammals. And these creatures' common origins
are still visible in their bodies. Just like us, they all have bodies
with four limbs--they're all tetrapods."

Neil Shubin jumps in
again: "What that means is that all these different creatures
are descended from a common ancestor which had something very similar,
or akin, to limbs."

"Just what was that
common ancestor," the narrator asks, "and how did it leave
the water 370 million years ago?" Shubin and his colleagues
find fossils in Pennsylvania suggesting that early tetrapods lived
in streams, while Cambridge University paleontologist Jenny Clack
finds fossils in Greenland suggesting that fish evolved limbs before
they left the water.See
. For the standard story, see:

Shubin points to the
fossil fish fin and human arm skeleton that we saw at the beginning
of the episode, and he notes the similarity in the arrangements
of their bones. According to the narrator: "With the basic
pattern in place, the fin-to-limb transition was merely a series
of small changes occurring over millions of years." And a cartoon
animation shows us how easy this might have been. But a cartoon
animation, no matter how plausible, does not show how real animals
in real time could have been transformed from fish into land animals.

Shubin continues: "There's
really no goal to evolution. Evolution wasn't trying to make limbs;
it wasn't trying to push our distant ancestors out of the water.
What was happening was a series of experiments." And the narrator
concludes: "Fish experimented with all sorts of survival strategies.
. . . The first tetrapods possibly found another way to survive"--by
getting out of the water.

So fish "experimented"
with survival "strategies" that included growing legs.
But clever human biologists have been experimenting with fish for
years, and they have not come up with a strategy to make fish grow
even the beginnings of legs. What sense does it make to say that
fish "experimented" with growing legs?

The truth is that scientists
don't know how the first legs--or the first tetrapods, or the first
air-breathers, or the first whales--originated. The fossils tell
us that aquatic animals preceded land animals, and that land animals
preceded whales. On the question of what caused these great transformations,
however, the fossils are silent.

But without knowing what
caused these great transformations, how can Shubin say with such
confidence that evolution had no goal? How does he know?

D. The Cambrian Explosion

As the camera pans over
the fossilized remains of ancient animals, the narrator says: "The
water-to-land transformation wasn't the first time evolution had
experimented with radical new forms of life. An even earlier explosion--perhaps
the most significant of all--occurred just over half a billion years
ago. This was the one that led to animal life itself."

Shubin elaborates: "Evolution
tinkered with fish to make limbs, but fish carry the baggage of
their own past. Think of a fish. It has a head, it has a tail, and
a bunch of fins in between. That's a body plan--the way the body's
put together. But that's just one of many ways of putting animals
together." We're shown pictures of jellyfish, a millipede,
a beetle, and a crab. "The question is: What sort of tinkering
led to these body plans? I mean really what we're dealing with here
is the origin of animals."

"According to the
fossil record," the narrator says, "animals burst upon
the earth rather suddenly," hundreds of millions of years ago.
"Scientists call this crucial transformation the Cambrian explosion."
Cambridge University paleontologist Simon Conway Morris explains:
"The Cambrian explosion was effectively one of the greatest
breakthroughs in the history of life. About half a billion years
ago, suddenly things change, we have this extraordinary explosion
of diversity. And this sudden appearance of the fossils led to this
term, the Cambrian explosion. Darwin, as ever, was extremely candid--he
said, Look, this is a problem for my theory. How is it that suddenly
animals seem to come out of nowhere? And to a certain extent that
is still something of a mystery."

It certainly is. In Darwin's
theory, all animals are descended from a common ancestor. If the
theory were true, we would expect the history of animal life to
begin with one form; as time passes, this form would give rise to
two or three that are only slightly different from each other; and
with more time, these would give rise to other forms, even more
different from each other. Finally, after millions of generations,
we would see the major differences that now separate clams from
starfish and insects from vertebrates.

The coverage of the Cambrian
explosion in this episode is better than one usually sees in treatments
of evolution. Most biology textbooks (including one co-authored
by Kenneth Miller, who played a prominent role in Episode One),
completely ignore the Cambrian explosion and the challenge it poses
to Darwin's theory. Evolution's producers deserve to be commended
for including it, though they largely ignore Simon Conway Morris's
comment that the Cambrian explosion "is still something of
a mystery," and thus pass up a chance to acquaint viewers with
the controversy surrounding one of evolution's most exciting unresolved
challenges.

Spectacular views of
the Canadian Rockies now follow--home of the famous Burgess Shale,
which has provided us with much of the best evidence for the Cambrian
explosion. After surveying some of the forms found in the Burgess
Shale, the narrator says: "All the basic body plans found in
nature today are here. Everything that has lived for the last half-billion
years came from tinkering with these initial designs. We can even
see our own ancestor here." Simon Conway Morris displays a
photograph of a tiny worm, Pikaia, and tells us "this might
be the precursor of the fish, and so also, I believe--after a long
evolutionary story--ourselves."

Neil Shubin returns to
summarize what we've seen so far: "So what do we learn by looking
at 600 million years of animal history? Evolution's tinkering with
mammalness to make whales; in the same way, it's tinkering with
fishiness to make tetrapods; and it's tinkering with animalness
to make all the different body plans that we see."

There's that "tinkering"
again. We've seen that animals burst upon the scene rather suddenly,
that land animals came later, and that whales came later still.
Things are certainly not what they used to be. But where is the
evidence that it all happened through "tinkering"?

Shubin continues: "All
these different creatures are variations of the same theme, re-stated
over and over again. The question was, What was evolution tinkering
with? One of the remarkable discoveries of the last twenty years
is that evolution's not tinkering with the bodies, it's tinkering
with the recipe, the machinery that builds bodies. What is that
recipe? What is that machinery? It's the genes, the genes that build
them."

Finally, we are promised
some hard evidence of how these great transformations took place.
Let's take a look at it.

E. The Genetic Mechanism
of Evolution

"Fossils record
the changes in animals' bodies over time," the narrator says,
"but just how bodies changed was
unknown. The search for the genetic mechanism of evolution took
most of the century. When scientists finally found it, they were
astonished by just how simple it was."

In the nineteenth century,
geneticist William Bateson had observed that embryos would occasionally
develop body parts in the wrong places. Then biologists in the 1940s
discovered that they could produce such effects in fruit flies by
using radiation. Stanford University developmental biologist Matthew
P. Scott explains that, like Bateson, these researchers would occasionally
find flies with "one part of the body in the wrong place, or
a copy of a normal part of the body in another place."

Watch closely as a fruit fly with an extra pair of wings fills
the screen. (Fruit flies normally have two wings, but this one has
four.) Note that the wing visible here behind the normal pair is
stiff and motionless. That's because the second pair of wings has
no muscles. The extra wings are thus useless, and the fly has difficulty
flying and mating--though that fact goes unmentioned here. Next
we see a mutant fly with no wings (which of course has even more
difficulty flying!), then a fly with stubby legs instead of antennae
growing out of its head. All three of these mutant flies are cripples,
and cannot survive long outside the laboratory.

"The scientists
had triggered the changes by damaging the fly's DNA," the narrator
says. He continues with an overview of how scientists in the past
quarter-century have unraveled some of the ways in which genes affect
embryo development. It's a fascinating story about painstaking research,
requiring considerable patience and perseverance, which finally
ended in success. One of those successes involved deciphering the
action of the Antennapedia gene, in which mutations can cause flies
to sprout legs from their heads. The narrator concludes that the
"implications were mind-boggling," because such genes
seemed to be "acting like architects of the body."

Could this discovery
be generalized to other animals? The scene switches to Switzerland,
where University of Basel cell biologist Walter Gehring describes
how he removed a gene from a fruit fly that is needed for normal
eye development, and inserted a comparable gene from a mouse. Gehring
found that the mouse gene did the work of the fly gene. "The
fruit fly had grown normal fruit fly eyes," the narrator explains,
"using a gene from a mouse. Not only did the two creatures
use the same mechanism--they used the very same gene. This was the
mechanism behind extra wings, legs sprouting from heads, and Bateson's
deformed animals. The century-long search was complete. The genetic
engine of evolution turned out to be a tiny handful of powerful
genes."

As we watch some more
beautiful wildlife photography, University of Wisconsin geneticist
Sean B. Carroll interprets the significance of this: "So what
this means is--in some ways, some sense--evolution is a simpler
process than we first thought. When you think about all of the diversity
of forms out there, we first believed that this would involve all
sorts of novel creations, starting from scratch, again and again
and again. We now understand that, no, that evolution works with
packets of information, and uses them in new and different ways
and new and different combinations without necessarily having to
invent anything fundamentally new, but new combinations."

As a series of brightly-colored
cartoons shows the supposedly similar body organization of various
kinds of animals, the narrator explains: "Suddenly, the commonality
of form among animals was understood. Animals resembled each other
because they all used the same set of genes to build their bodies--a
set of genes inherited from a common ancestor that lived long ago."
Matthew Scott adds: "And what we see now among all the animals
are just variations on a body plan that existed half a billion years
ago."

"And there's only
one inescapable conclusion you can draw from that," says Carroll,
"which is: If all of these branches have these genes, then
you have to go to the base of that, which is the last common ancestor
of all animals, and you deduce it must have had these genes. So
the whole radiation of animals, the whole spring of animal diversity
has been fed by essentially the same set of genes."

What's wrong with this
picture? The story we have just heard ignores two fundamental problems.
The first is that (as we saw above) the genetic changes shown here
are--without exception!--harmful to the organism. In the wild, all
of these changes would be quickly eliminated by natural selection.
Geneticists have learned a lot about how genes affect embryo development,
but they have not yet found a single mutation that changes the shape
of an animal's body in a way that might be useful for evolution
outside the laboratory. (Useful mutations occur in some cases of
antibiotic resistance, as we shall see in Episode Four; but that's
a far cry from changing the shape of an animal's body.)

The second problem is
that the "tiny handful of powerful genes" is nowhere near
as powerful as we are led to believe. Note that the mouse eye gene
inserted into the fruit fly produced a fruit
fly eye, not a mouse eye. In other words, the gene was not
the "architect" of the eye; it merely acted as a switch,
enabling the animal to make an eye when and where it needed one.
But the gene has nothing to do with the kind of eye the animal makes.
It's more like an electrical switch that can turn on a light, a
computer, a vacuum cleaner--or whatever else is plugged into it.
If these genes are what animals use to "build their bodies,"
and if all animals have the same set of genes, how come the various
kinds of animals are so different from each other? Why don't fruit
flies give birth to finches?

Once again, we are left
without the evidence we were hoping to see. Instead, we are simply
assured that evolution is simpler than we thought, and given the
same line that modern animals are simply variations of an ancestral
body plan that existed long ago.

F. From Ape to Human

"What about us?"
the narrator asks. "Our bodies are built from the same genes
that build all other animals. Yet we are different. No other animal
designs or creates like we do." The camera pans slowly over
Michelangelo's Sistine Chapel painting of God touching Adam. The
narrator continues: "We seem so special, it's hard not to think
that we're somehow an exception to evolution. But of course we're
not. The transformation that led to us was no different from the
others." In a familiar scene (which is repeated again and again
throughout the series), an ape clambers down a log to the ground.
"The crucial turning-point seems to have occurred about seven
million years ago, when our ancestors left the trees and began to
walk on two legs."

According to Arizona
State University paleoanthropologist Donald Johanson, this probably
first happened in East Africa. He and the narrator explain how walking
on two feet seems to have opened the door to the evolution of our
brains, though little is known about how our ancestors became bipeds.
University of Texas anthropologist Liza J. Shapiro tries to answer
this question by studying lemurs, because "we have to know
what it was we started from." The narrator explains: "Like
lemurs, our early ancestors could move in all sorts of ways."
So "they were already adapted to so many movement styles, they
could serve as the starting-point for a variety of evolutionary
experiments. And that's just what happened."

After being assured that
we evolved from a lemur-like animal, and that the striking similarities
between chimps and us show that we only recently evolved from a
common ancestor, we are told that "the few physical differences
that set us apart seem to have made a great difference." Johanson
points out some of them on models of human and chimp skeletons,
and concludes: "These are minor differences. These are the
sorts of tinkering that evolution did to change us into a modern
biped." So "what we see is that evolution has worked the
same way with us as it has with every single organism on this planet.
We're here through a series of chance coincidences, specific adaptations,
chosen opportunities."

Words like "tinkering"
and "chance" clearly mean something other than what Michelangelo
painted on the ceiling of the Sistine Chapel. But--once again--where
is the evidence? That we are "built from the same genes that
build all other animals"? That lemurs can "move in all
sorts of ways"? That there are both similarities and differences
between humans and chimps?

The truth is that the
evidence for human origins is even weaker than some of the other
evidence we've seen. According to Henry Gee, chief science writer
for Nature, all the evidence for human evolution "between about
10 and 5 million years ago--several thousand generations of living
creatures--can be fitted into a small box." Thus the conventional
picture of human evolution as lines of ancestry and descent is "a
completely human invention created after the fact, shaped to accord
with human prejudices." Putting it even more bluntly, Gee concludes:
"To take a line of fossils and claim that they represent a
lineage is not a scientific hypothesis that can be tested, but an
assertion that carries the same validity as a bedtime story--amusing,
perhaps even instructive, but not scientific."See
. For the Gee quotations see: Henry Gee, In Search of Deep Time
(New York: The Free Press, 1999), 23, 32, 113-117, 202.

So Episode Two, instead
of showing us the "underlying evidence" for Darwin's theory,
leaves us with a bedtime story.

Notes

.
Not surprisingly, the actual story of whale-like fossils is not
as neat as the one told here. There are long-standing disputes
over the identity of the land ancestor, the geological position
of various fossils, and whether these were the ancestors of modern
whales. Modern molecular studies have added to the controversy.
For a short survey of some of the disputes, see Ashby L. Camp,
"The Overselling of Whale Evolution," available at:

http://www.trueorigins.org/whales.htm#top.

See also:

http://www.sciencenews.org/sn_arc98/10_10_98/Fob3.htm

For more
on how modern molecular studies have added to the controversy,
see Trisha Gura, "Bones, molecules . . . or both?" Nature
406 (2000), 230-233; Maureen A. O'Leary, "Parsimony Analysis
of Total Evidence from Extinct and Extant Taxa and the Cetacean-Artiodactyl
Question (Mammalia, Ungulata)," Cladistics 15 (1999), 315-330.
See also:

http://www.findarticles.com/m1200/19_156/57828404/p1/article.jhtml

On the impossibility
of inferring ancestor-descendant relationships from fossils see
Henry Gee, In Search of Deep Time (New York: The Free Press, 1999).
Some passages from Gee's book that deal with human evolution are
cited below in the note on human origins.

On the fact
that mere similarity is insufficient to establish Darwinian descent
with modification, see Jonathan Wells and Paul Nelson, "Homology:
A Concept in Crisis," available at:

http://www.arn.org/docs/odesign/od182/hobi182.htm

Of course,
the true story is more complicated than the one presented in this
episode; see Michel Laurin, Marc Girondot and Armand de Ricqlès,
"Early tetrapod evolution," Trends in Ecology and Evolution
15 (2000), 118-123.

The "tinkering"
metaphor comes from François Jacob, "Evolution and
Tinkering," Science 196 (1977), 1161-1166. According to Jacob,
an engineer works according to a preconceived plan, uses prepared
materials and special machines, and produces things that are as
nearly perfect as possible. Evolution, on the other hand, has
no plan, works with whatever is at hand, and produces things that
are imperfect. But a tinkerer still works according to a plan,
though it may be a short-range plan (i.e., to make something useful);
and the history of technology is filled with examples of engineered
products that were notably imperfect. Most importantly, the sort
of creative capacity attributed to natural selection by the tinkering
metaphor has never been observed in nature.

.
Darwin wrote in The Origin of Species that "if the theory
be true, it is indisputable that before the lowest Cambrian
stratum was deposited long periods elapsed . . . [in which]
the world swarmed with living creatures." Yet he acknowledged
that "several of the main divisions of the animal kingdom
suddenly appear in the lowest known fossiliferous rocks."
Darwin called this a "serious" problem which "at
present must remain inexplicable; and may be truly urged as
a valid argument against the views here entertained." (Chapter
X; page numbers will vary depending on the edition.)

Simon Conway
Morris has written about the Burgess Shale in The Crucible of
Creation: The Burgess Shale and the Rise of Animals (Oxford: Oxford
University Press, 1998). So has Stephen Jay Gould, in Wonderful
Life: The Burgess Shale and the Nature of History ((New York:
W. W. Norton, 1989). See also Simon Conway Morris and H. B. Whittington,
"The Animals of the Burgess Shale," Scientific American
241 (1979), 122-133; Mark and Dianna McMenamin, The Emergence
of Animals: The Cambrian Breakthrough (New York: Columbia University
Press, 1990); Jeffrey S. Levinton, "The Big Bang of Animal
Evolution," Scientific American 267 (1992), 84-91; and J.
Madeleine Nash, "When Life Exploded," Time (December
4, 1995), 66-74.

For a more
extended discussion of the challenge posed by the Cambrian explosion
to Darwin's theory, see Jonathan Wells, Icons of Evolution (Washington,
DC: Regnery Publishing, 2000), Chapter 3. In contrast, one biology
textbook that covers the topic of evolution but manages to ignore
the Cambrian explosion completely is Kenneth R. Miller and Joseph
Levine, Biology (Upper Saddle River, NJ: Prentice-Hall, 2000).

.
For a detailed discussion of the problems with using four-winged
fruit flies as evidence for evolution, see Jonathan Wells, Icons
of Evolution (Washington, DC: Regnery Publishing, 2000), Chapter
9.

For some
general critiques of the idea that "genes build bodies,"
see H. F. Nijhout, "Metaphors and the Role of Genes in Development,"
BioEssays 12 (1990), 441-446; Brian Goodwin, How the Leopard Changed
Its Spots (New York: Charles Scribner's Sons, 1994); Steven Rose,
Lifelines (Oxford: Oxford University Press, 1997); and Jason Scott
Robert, "Interpreting the homeobox: metaphors of gene action
and activation in development and evolution," Evolution &
Development 3:4 (2001), 287-295.

According
to paleoanthropologist Misia Landau, many writings in her field
have been "determined as much by traditional narrative frameworks
as by material evidence." The typical framework is that of
a folktale in which a hero (i.e., our ancestor) leaves a relatively
safe haven in the trees, sets out on a dangerous journey, acquires
various gifts, survives a series of tests, and is finally transformed
into a true human being. When paleoanthropologists want to explain
what really happened in human evolution they use four main events.
These are: moving from trees to the ground, developing upright
posture, acquiring intelligence and language, and developing technology
and society. Although Landau found these four elements in all
accounts of human evolution, their order varied depending on the
viewpoint of the narrator. She concluded that "themes found
in recent paleoanthropological writing . . . far exceed what can
be inferred from the study of fossils alone and in fact place
a heavy burden of interpretation on the fossil record--a burden
which is relieved by placing fossils into preexisting narrative
structures." Narratives of Human Evolution (New Haven, CT:
Yale University Press, 1991), ix-x, 148.

In 1997,
Arizona State University anthropologist Geoffrey Clark wrote that
"we select among alternative sets of research conclusions
in accordance with our biases and preconceptions--a process that
is, at once, both political and subjective." Clark suggested
"that paleoanthropology has the form but not the substance
of a science." G. A. Clark and C. M. Willermet (eds.), Conceptual
Issues in Modern Human Origins Research (New York: Aldine de Gruyter,
1997), 76.